This invention relates in general to small sailing craft, and more particularly to sailboards of the type employed by windsurfers. Even more particularly this invention relates to a planing type of sailboard having an adjustable keel mechanism for directing the sailboard along a path extending substantially in the direction of the longitudinal axis of the sailboard.
Sailboards are currently the fastest and most maneuverable type of sailing boat. The fastest designs have the usual, generally flat, planing-type hull, and a single, fixed keel, which normally is disposed in a vertical plane through the longitudinal centerline of the hull to provide the necessary lift to windward for sailing. As a general rule there are no pivotal rudders or other hydrofoils on the hull.
However, despite great experimentation with hull and keel shapes, a plateau has been reached in the achievement of top speeds. The current record speed is approximately 38 knots. Many hull designs achieve speeds close to that limit but have not been able to exceed it. The plateau is not due to sail inefficiency alone, since ice and land sailing vessels of similar configuration and sail design are capable of much higher speeds than sailboards or a sailboats in general.
At present the greatest limitation on high-speed sailboard performance arises from the necessity of holding the keel, and consequently the hull, at an angle to the oncoming water-flow in order to generate lift. Just as in the case of an airfoil, a hydrofoil produces lift only when it has an angle of attack to the ambient flow. Thus, for a conventional sailboard to accelerate or maintain speed on any point of sail, except dead downwind, the hull and its fixed keel must move obliquely, or "make leeway".
The oblique movement of the hull leads to problems at high speed. First, the hull cannot be shaped to plane with the least possible drag, since it must be a compromise between two angles of operation, normally differing by approximately ten degrees. For example, when a concave channel on the hull bottom is oriented to increase planing efficiency on one tack, it will be incorrectly oriented on the other tack. As a consequence, conventional sailboards are not as fast as they could be if the hull were to be caused to move or sail exactly in the direction of its longitudinal axis, when planing. Secondly, at high speeds rough water generally makes control of a conventional sailboard difficult. The reason for this is the need to keep a relatively large hull at a constant, oblique orientation to the oncoming water, even as the degree of submersion varies from substantial to none. Obviously it would be easier to control a hull that tracks straight through rough water, for example at right angles to the oncoming water.
Prior to this invention, sailboards could not be sailed in such manner that their hulls would sail or move in a direction substantially coincident with the longitudinal axis of the hull on both tacks, or in other words without crabbing, or moving obliquely. U.S. Pat. No. 4,478,164, for example, sought to improve the performance of a sailboard by using an improved universal joint for supporting two pivotal masts, and by adding to the stern of the board a pivotal rudder connected by a steering mechanism to one of the sails. This sailboard, however, like most conventional sailboards, also utilizes a stationary (during use) centerboard or keel, which functions in the usual manner to minimize leeward drift, and to enable the bow to be held at the necessary angle of attack to the oncoming water flow. A similar construction is taught by U.S. Pat. No. 4,539,926, which again discloses a board-like floating body or planing board having a conventional centerboard or fixed keel or daggerboard, and a pivotal rudder for steering. Each of these sailboards is thus designed for oblique sailing.
U.S. Pat. No. 4,441,446 also discloses a sailboard, or windsurfing board, which utilizes a stationary centerboard or keel. However, instead of also using a pivotal rudder of the type disclosed by the two above-discussed patents, the board as disclosed in this particular patent uses a pair of rectangular fin plates, which project from opposite sides of the hull of the board, and which are adjustable vertically by a foot pedal to position them under the surface of the water to improve planing properties in a heavy wind, or above the water level during a light wind.
U.S. Pat. No. 4,331,093 discloses a hybrid wind surfboard or sailboard comprising two or more conventional surfboards which are linked or assembled together in tandem fashion. Each board has a conventional, fixed daggerboard keel located midship, and a stationary stabilizing fin at the stern of the board.
A feature common to all of the sailing devices disclosed in the above-noted U.S. patents is the fact that each sailboard or windsurfing board is of the type having a planing hull, which tends to skim the water surface, rather than displacing a substantial amount of water. This contrasts with conventional sailboats, which as a general rule are substantially heavier than sailboards and have hulls that are specifically shaped and designed to displace water, or to penetrate deeply down into the water, when sailing. Conventional sailboats are thus designed for oblique sailing, and for that reason require both pivotal rudders at their sterns, and centerboards or keels amidship.
Efforts have been made to improve the sailing speed of conventional sailboat hulls by using adjustable centerboards which are mounted to pivot above vertical axes. The centerboard disclosed in U.S. Pat. No. 3,580,203, for example, is free to pivot in the water against the resistance of a spring, while the centerboard shown in U.S. Pat. No. 4,345,535 is operatively connected to a mast which rotates the centerboard in response to any tilting of the mast. In each such case, however, the pivotal centerboard must be used in combination with the pivotal rudder to offset the tendency of the hull to make headway to leeward during sailing.
It will thus be apparent that while efforts have been made to stabilize sailing conditions for displacement-type hulls by utilizing adjustable centerboards, no such construction has been designed for planing-type hulls. Moreover, even when sailboat hulls have incorporated adjustable keels, it has always been in concert with, or in combination with, a pivotal rudder at the stern of the hull in order to effect the desired steering. Moreover, in most instances these prior devices have tended to be rather complicated in structure and in operation.
It is an object of this invention, therefore, to provide a novel, planing-type sailboard which utilized an adjustable keel, or centerboard or daggerboard, but without the use of a complimentary rudder for effecting the steering of the board.
A more specific object of this invention is to provide for a planing craft or sailboard, a single, pivotal keel mechanism which is relatively simple and inexpensive to manufacture, to install, and to use.
Still a further object of this invention is to provide an adjustably-keeled sailboard of the type described, which is adapted to be operated in the same manner as a conventional sailboard, and which has a pivotal, spring-loaded keel mechanism the position of which is automatically changed for each tack by virtue of the normal operator movements.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.